United Airlines refund policy is as follows:

If you buy a ticket at least one week before departure and cancel within 24 hours of purchase, you will not be charged a cancellation fee and will receive a full refund.

Outside of the 24-hour timeframe, Basic Economy tickets cannot be reimbursed. This implies you must have purchased your ticket at least 7 days before travel and canceled it within 24 hours.

Refunds for credit card transactions will be processed within 7 business days of receiving your request. Other refund requests will be processed within 20 business days.